Resnatron filament basket



Allg 14. 1956 w. H. Kol-n.

REsNATRoN FILAMENT BASKET Original Filed Sept. 2l. 1950 INVEN TOR. M :new Af awz United States Patent O RESNATRON FILAMENT BA'SK'ET Walter H. Kohl, Cedar Rapids, Iowa, assignor to Collins 'Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Original application September 21, 1950, Serial No. 186,038, now Patent No. 2,662,990, dated December '15, 1953. Divided and this application October 20, 1951, Serial No. 252,255

1 Claim. (Cl. 29--25.18)

This invention relates to a resnatron filament basket.

This invention is a division of application No. 186,03 8, filed September 2l, 1950, Patent No. 2,662,990, issued December 15, 1953, entitled, Resnatron Filament Basket.

The electronic device known as a resnatron requires a concentric filament which gives an unusually large amount of emission. Filament baskets have been used which comprise staples of tungsten that are mounted in holding rings at either end. The end rings are usually liquid cooled. Cooling of the end rings results in an emission loss for the reason that heat flows from the hot emitting portion to the rings. This is undesirable. Another problem encountered in the fabrication of resnatron filament baskets is that the emitting portion of the basket tends to bow and become misaligned because of thermal expansion.

It is an object of this invention, therefore, to provide a resnatron filament basket in which the thermal expansion of the emitting portion is compensated to prevent misalignment.

Another object of this invention is to provide a hot resnatron lament basket wherein the portions of the basket adjacent the emitting part are maintained at a relatively high temperature and, thus, end cooling of the active portion is prevented.

Still another object of this invention is to provide a resnatron filament basket which may be formed as a unitary structure from the same material which forms the emitting portions.

Still another object of this invention is to provide a composite resnatron filament basket which is formed by spinning about a soft low melting point core.

A feature of this invention is found in the provision for a resnatron filament basket comprising a plurality of center emitting segments that are integrally formed with a lower and upper end portion. An expansion member is attached to the upper portion and compensates for thermal expansion of the basket.

Further objects, features and advantages of this invention will become apparent from the following description and claim when read in view of the drawings, in which:

Figure 1 is a perspective View of the resnatron filament basket of this invention;

Figure 2 is a side view showing how the filament basket is spun about a mandrel; and,

Figure 3 is a view showing how the emitting portions are milled into the resnatron filament basket.

Figure 2 illustrates a mandrel 10 which is formed from metal which has a relatively low melting point. It is mounted on the shaft 11 which may be mounted in suitable bearings and connected to a driving means as, for example, a lathe. A cylinder 12, of tantalum or tungsten, is mounted axially of the mandrel 10 and a spinning tool 13 is used to form the cylinder 12 to the shape of the mandrel 10. After one end 14 of the filament basket has been shaped, the opposite end 16 is spun. Figure 3 illustrates the filament basket 12 after it has been spun to the shape of the finished basket. The shaft 11 is rigidly mounted in a milling machine anda cutting tool 17 is used to form a plurality of emitting sections 18 in the basket. The mandrel 10 is cut by the tool 17 and gives a steady backing to the thin cylinder 12 as it is cut.

After the emitting strips 18 have been formed with the cutting tool 17, ythe cylinder 12- and the mandrel 10 are subjected to temperature which is high enough to melt the mandrel 10. The cylinder 12 which -may be formed of tantalum or tungsten has a high melting point, and therefore remains intact as the mandrel melts and runs out of the lament lbasket thus formed.

Figure 1 shows the cylinder 12 with an expansion member mounted therein after it has been freed of the mandrel. A coaxial base member 19 comprises an outer support 21 and an inner support 22. The outer support 21 is formed with liuid passageways 23 through which a cooling fluid is circulated. The center support 22 is hollow and has a standpipe 24 mounted therein. Cooling fiuid is supplied to the standpipe 24 and passes out through the space between the members 22 and 24. Mounted to the end of the inner support member 22 is a rod 26 which has its upper end connected to a disc 27. The disc 27 may be made of tantalum or tungsten and has its outer edge 28 welded to a rim 29 formed in the cylinder 12 during the spinning process. A heat shield 31 fits concentrically about the rod 26 and is attached to the disc 27. It extends substantially the entire length of the rod 26.

An adapter 32 is connected to the top end of the outer connector 21 by welding and has its top end welded to the cylinder 12. The member 32 may be made of tantalum or tungsten and has a relatively high melting point. A center opening 33 is formed therein to allow the rod 26 to pass therethrough. A heating potential which may be direct current or relatively low frequency alternating current is supplied between the outer conductor 21 and the inner conductor 22 and current fiows between the two conductors by passing through the rod 26 to the disc 27 and hence into the transitional section 34 of the cylinder 12. From the transitional section 34 the current fiows through the emitting portions 18, to a lower transitional portion 36, and to the member 21 through the adapter 32.

The rod 26 is out of a material such that when thermal expansion occurs in the portions 36, 34, and 18 it will expand an equal amount and thus prevent misalignment and buckling of the active sections 18. The active portion 18 of the basket should operate at about 2200 degrees Kelvin and the heat shield 31 allows the rod 26 to operate at a much lower temperature as, for example, 550 degrees Kelvin. If copper is used for the center rod 26 and it is operated at 550 degrees Kelvin it will expand the same amount as the basket wherein the active portions 18 are operating at 2200 degrees Kelvin and the transition members at a lower temperature as, for example, 1300 degrees Kelvin. It is to be understood, of course, that the transition members 34 and 36 will have a temperature gradient from very hot adjacent the active portions 18 to the coolest portions adjacent the ends.

It is seen that applicants invention provides a resnatron filament basket which is integrally formed by spinning about a low melting point mandrel, machining the active portions, and mounting an expansion center post through the basket to compensate for thermal expansion. The results are an improved basket in which misalignment is greatly decreased. Another advantage obtained is that since the transition members 34 and 36 are made of tantalum or tungsten they need not be liquid cooled and thus the active portions 1S are not subjected to a great deal of end cooling. A high degree of emission is obtained, therefore, over their entire active lengths. The entire assembly will operate at a higher temperature and the heat shield 31 will prevent the rod 26 from reaching too high a temperature. The heat shield 31 is made from tantalurn or other material which has a high melting point so that it does not melt at the high operating temperature.

Although this invention has been described with respect to the particular embodiments thereof, it is not to be so limited as changes and modications may be made therein which are Within the full intended scope of the invention as defined by the appended claim.

I claim:

A method of forming a resnatron filament basket comprising, placing a metal cylinder of a high melting point over a low melting-point mandrel having reduced end portions, spinning the end portions only of said cylinder to the shape of the mandrel, milling a plurality of Slots in the center portion of said cylinder and mandrel, heating said cylinder and mandrel to a temperature high enough to melt outfthe mandrel, inserting into the formed cylinder a disc with a rod extending therefrom, and Welding the periphery of said disc to one reduced end of said cylinder.

References Cited in the file of this patent UNITED STATES PATENTS 264,150 Grom Sept. 12, 1882 285,574 Clarke Sept. 25, 1883 303,222 Grom Aug. 5, 1884 1,994,767 Heintz Mar. 19, 1935 2,306,925 Aicher Dec. 29, 1942 2,468,736 Butler May 3, 1949 2,565,623

Parker Aug. 28, 1951 

